1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine or a printer. More particularly, the invention relates to an image forming apparatus with a plurality of fixing devices and a fixing unit for use with the image forming apparatus.
2. Description of the Related Art
There has been proposed an image forming apparatus having a plurality of fixing devices.
In the image forming apparatus, for example, a plurality of fixing devices are disposed in parallel along a traveling direction of a recording material to selectively change the fixing devices in use (e.g., JP-A-2000-221834).
In this type of the image forming apparatus, even in a consecutive recording operation, there is no need to wait until the temperature of the fixing device rises halfway through a consecutive recording operation. Accordingly, the apparatus is capable of performing the recording operation at high speed.
In the image forming apparatus according to the related art having the plurality of fixing devices, those fixing devices are not the ones specially designed for recording an image at high quality. Accordingly, the image forming apparatus is incapable of recording the image at high quality.
As means for solving such a problem, a technique (for example, JP-A-Hei.10-123863) can be applied in which in order to obtain a photographic image, a special toner is used to vary the fixing speed, the fixing pressure, the fixing temperature, and the like in a fixing step.
However, in this type of the related art, since the recording material always passes through the plurality of fixing devices, excessive fixing is performed for recording in the normal image quality, thereby impairing the productivity.
As a related art for obtaining the high image quality by using the normal toner, a technique (for example, JP-A-Hei.6-258970) has been proposed in which a plurality of fixing devices are disposed in parallel along a transporting path of a recording material and the recording material is passed through nip regions of both fixing devices in order to improve the fixing property.
However, in this type of the related art, since the recording material always passes through the plurality of fixing devices, excessive fixing is performed for recording in the normal image quality. Therefore, it is concerned to impair the productivity.
More specifically, in a case of forming an image having the high image quality such as a photographic image on a recording material, generally, there are fewer requests to form the image having the high image quality on both sides of the recording material. For example, in a case of preparing a post card photographic-printed, in most cases, it is sufficient only have to form an image having the normal image quality on one side of the recording material so long as the image having the high image quality such as a photographic image is formed on the other side of the recording material.
Under this circumstance, when a post card is prepared on one side of which a photo is printed, for example, in a both-side recording mode, in spite of being allowed to form an image having the normal image quality on a side of the post card where the photo is not printed, a plurality of fixing devices perform the fixing process. Therefore, not only excessive fixing process is performed, but also since the post card always passes through the plurality of fixing devices, the productivity in a one-side recording mode can be impaired.
The invention has been made to solve the above described technical problems. According to an aspect of the invention, there is provided an image forming apparatus comprising:
an image forming module for forming images on both sides of a recording material sequentially; and
a fixing device for fixing the images on both sides of the recording material,
wherein the fixing device includes a primary fixing device disposed in a recording material transporting path and a secondary fixing device disposed in the downstream of the primary fixing device; and
the recording material is passed through only the primary fixing device after an image is recorded on a front surface of the recording material, an image is recorded on a rear surface of the recording material, and subsequently, the recording material is passed through the primary fixing device and the secondary fixing device.
Accordingly the image quality is well maintained in the high image quality and the productivity can be improved.